A new method to perform the cover test.

A new method is presented to perform the cover/uncover test and the alternate cover test. With the subject's head in a chin rest, he fixates an object at either near or far distance, and one eye is illuminated from above with a collimated infrared beam. A high-sensitivity infrared TV camera observes the first and fourth Purkinje images from below. The examiner covers the nonilluminated eye and, viewing a TV monitor, compares the relative positions of the two images before and after covering. By changing the incident angle of the beam, the amount of deviation can be measured. To perform the alternate cover test, the illuminated eye is covered with an infrared transmitting filter.